Development of anti-aflatoxin B1 nanobodies from a novel mutagenesis-derived synthetic library for traditional Chinese medicine and foods safety testing

BACKGROUND

The main commercially available methods for detecting small molecules of mycotoxins in traditional Chinese medicine (TCM) and functional foods are enzyme-linked immunosorbent assay and mass spectrometry. Regarding the development of diagnostic antibody reagents, effective methods for the rapid preparation of specific monoclonal antibodies are inadequate.

METHODS

In this study, a novel synthetic phage-displayed nanobody Golden Glove (SynaGG) library with a glove-like cavity configuration was established using phage display technology in synthetic biology. We applied this unique SynaGG library on the small molecule aflatoxin B1 (AFB1), which has strong hepatotoxicity, to isolate specific nanobodies with high affinity for AFB1.

RESULT

These nanobodies exhibit no cross-reactivity with the hapten methotrexate, which is recognized by the original antibody template. By binding to AFB1, two nanobodies can neutralize AFB1-induced hepatocyte growth inhibition. Using molecular docking, we found that the unique non-hypervariable complementarity-determining region 4 (CDR4) loop region of the nanobody was involved in the interaction with AFB1. Specifically, the CDR4's positively charged amino acid arginine directed the binding interaction between the nanobody and AFB1. We then rationally optimized the interaction between AFB1 and the nanobody by mutating serine at position 2 into valine. The binding affinity of the nanobody to AFB1 was effectively improved, and this result supported the use of molecular structure simulation for antibody optimization.

CONCLUSION

In summary, this study revealed that the novel SynaGG library, which was constructed through computer-aided design, can be used to isolate nanobodies that specifically bind to small molecules. The results of this study could facilitate the development of nanobody materials to detect small molecules for the rapid screening of TCM materials and foods in the future.

Lack of protective effect by intermittent hypoxia on MPTP-induced neurotoxicity in mice

In the study we report here, several lines of evidence support the preventive action of intermittent hypoxia against oxidative injuries in CNS. Our in vitro data showed that autooxidation and iron-induced lipid peroxidation were attenuated in cortical homogenates of intermittent hypoxia-treated animals. Furthermore, our preliminary study found that iron induced oxidative injuries were abolished in rat brain after intermittent hypoxic treatment (paper submitted). Several antioxidative defensive systems improve in response to intermittent hypoxia. Since attenuation of autooxidation and iron-induced lipid peroxidation were observed in cortical homogenates of intermittent hypoxia-treated mice, the lack of prevention by intermittent hypoxia of MPTP-induced neurotoxicity may be due to the MPTP action that is not oxidative related. Together with our previous studies, in which several antioxidants were shown to successfully prevent oxidative injuries, our data here suggest that intermittent hypoxia may offer a potential treatment for preventing CNS degenerative diseases.

Biliary cancer growth factor pathways, cyclo-oxygenase-2 and potential therapeutic strategies

Cholangiocarcinoma is a hepatic biliary cancer of high morbidity and mortality, whose molecular pathogenesis is unknown. However, there is increasing evidence to suggest that alterations in selected growth factor pathways, including an overexpression of the growth factor receptor tyrosine kinases c-ErbB-2/c-Neu and c-Met, together with possible aberrant autocrine expression of hepatocyte growth factor/scatter factor, the ligand for c-Met, may be playing important roles associated with the development of cholangiocarcinoma in both the human liver and in the furan rat model of cholangiocarcinogenesis. Cyclo-oxygenase-2, whose regulation has been experimentally related to c-ErbB-2/c-Neu as well as to hepatocyte growth factor/scatter factor, and which has been demonstrated to be overexpressed in other cancers of the gastrointestinal tract, has also been observed in preliminary studies to be upregulated in human biliary cancers and in cholangiocarcinoma induced in the furan rat model. Moreover, new data from our laboratory have demonstrated the cyclo-oxygenase-2 inhibitor NS-398 to produce a significant dose-dependent growth inhibition of rat cholangiocarcinoma cells in vitro, as well as to suppress anchorage-independent growth of these cells in soft agar. Based on the data reviewed, we propose that the selective therapeutic targeting of aberrant growth factor receptor tyrosine kinase signaling and of cyclo-oxygenase-2, alone or in combination, has potential to become a useful new approach for the treatment and/or chemoprevention of cholangiocarcinoma. We further propose that the furan rat model may serve as a powerful preclinical model for testing therapeutic and chemopreventative strategies that selectively target c-ErbB-2/c-Neu, cyclo-oxygenase-2, and/or autocrine hepatocyte growth factor/c-Met, aberrantly expressed in cholangiocarcinogenesis.

Unique epithelial cell production of hepatocyte growth factor/scatter factor by putative precancerous intestinal metaplasias and associated "intestinal-type" biliary cancer chemically induced in rat liver

Recently, we observed that Met, the receptor for hepatocyte growth factor/scatter factor (HGF/SF), is overexpressed in epithelial cells of both early-appearing intestinal metaplastic glands in precancerous hepatic cholangiofibrotic tissue and neoplastic glands in later developed intestinal-type of cholangiocarcinoma originated from the furan rat model of cholangiocarcinogenesis when compared with normal and hyperplastic intrahepatic biliary epithelia. We now show that HGF/SF is also aberrantly expressed in a manner closely paralleling that of its receptor in the neoplastic epithelial cells of furan-induced rat cholangiocarcinomas and in a majority of metaplastic epithelial cells within earlier formed precancerous hepatic cholangiofibrotic tissue. Using in situ hybridization and reverse transcription-polymerase chain reaction (RT-PCR), we further showed specific expression of HGF/SF messenger RNA (mRNA) in a novel rat cholangiocarcinoma epithelial cell line overexpressing Met. This cholangiocarcinoma cell line, termed C611B, was established from tumorigenic cells isolated from a furan-induced transplantable tumor. Moreover, we detected by in situ hybridization strong expression of HGF/SF mRNA transcripts in the cancerous epithelial glands of cholangiocarcinoma developed in recipient rats after in vivo cell transplantation of C611B cells. In contrast, mRNA transcripts and protein immunoreactivity for this cytokine were not detected in hepatocytes and biliary epithelial cells in adult normal rat liver nor in rat hyperplastic intrahepatic biliary epithelium. Our results clearly show that HGF/SF becomes aberrantly expressed in cholangiocarcinoma epithelium and in putative precancerous intestinal metaplastic epithelium induced in the liver of furan-treated rats.

Establishment of a novel rat cholangiocarcinoma cell culture model

Furan cholangiocarcinogenesis in rat liver is proving to be a unique and useful animal model for investigating important aspects of the cellular and molecular pathogenesis of cholangiocarcinoma potentially relevant to the human disease. We now describe the first culture model of rat cholangiocarcinoma cells derived from a transplantable cholangiocarcinoma originally induced in the liver of a furan-treated rat. An epithelial cell isolate highly enriched in viable cholangiocarcinoma cells was consistently obtained from transplantable cholangiocarcinoma tissue utilizing a similar procedure to that recently developed by us to establish a new rat hyperplastic bile ductular epithelial cell culture model characterized by the appearance of polarized bile ducts in vitro. Primary cholangiocarcinoma cell cultures could be readily established with these isolated cells and, in addition, we established from one such culture a novel rat cholangiocarcinoma cell line designated C611B. Cultured C611B cholangiocarcinoma cells retained a number of important characteristic features of the carcinoma cells of the parent tumor, including marked expression of the tyrosine kinase growth factor receptor proteins c-Met and c-Neu. Under basal culture conditions, the C611B cell line exhibited a cell doubling time of approximately 24 h and was aneuploid, with a predominant chromosomal count of 43. Moreover, C611B cells on collagen gels were 100% tumorigenic when transplanted into inguinal fat pads of syngeneic rats. All tumors formed at the transplantation site were cytokeratin 19-positive, mucin-producing tubular adenocarcinomas whose histological and phenotypic features closely resembled those of the furan-induced parent transplantable rat cholangiocarcinoma. Based on our findings, we believe that this novel rat cholangiocarcinoma cell culture model can serve as a valuable resource for investigating aberrant growth properties and tumor progression in biliary cancer.